A key federal advisory panel this week is expected to begin considering an unprecedented ban on salmon fishing in California in response to an alarming collapse of a signature fishery.

Salmon populations are depressed from the Bay Area to Washington state, but the problem is particularly acute for California's most productive run -- the Sacramento River fall run, which produces more than 80 percent of the salmon caught off the California coast.

Not only did numbers plunge steeply and unexpectedly last year, but a key indicator suggests things could be much worse a year from now.

"The situation is unprecedented and off the charts," said Donald McIsaac, executive director of the Pacific Fishery Management Council.

Though many researchers are pointing the finger at adverse ocean conditions, McIsaac and others say fluctuations in the ocean's currents and surface temperatures alone do not explain the problems.

And that is focusing renewed attention on the Delta and California's water delivery system, which is already being blamed at least partially for the ongoing collapse of several other fish species.

"I don't think you can say it's just ocean," McIsaac said.

McIsaac cautioned that the cause of the salmon collapse remains a mystery and that researchers have a list of 46 potential factors to investigate.

That list includes everything from disease, hatchery problems and an increase in predators to water diversions and a possible connection between the salmon collapse and the Delta's ongoing ecological crisis.

"People will be looking at that," he said, adding, "There's no obvious single smoking gun."

The fishery management council, which meets through Friday in Sacramento, is expected to discuss the California salmon collapse on Tuesday with the goal of proposing three options for the fishing season by the end of the week. A final decision is expected during its April meeting in Seattle.

It is widely anticipated that one option will be closing the salmon season entirely, a drastic move that has never happened on the West Coast. The closest the council got was two years ago, when the commercial fishing season was cut by two-thirds to protect Klamath River salmon that had been battered by poor habitat and upstream water diversions.

"I don't know if they have any choices," said Zeke Grader, executive director of the Pacific Federation of Fishermen's Associations. "As some of my guys have said, even if they give us a season, so what? There's no fish to catch."

"This is the first time we've seen one of our strong stocks collapse," Grader added.

Last year, state economists estimated the economic effect of recreational and commercial salmon fishing in California was about $20 million, a major decline from an industry that produced $100 million in the late 1970s and more than $40 million in the late 1990s.

Meanwhile, the commercial salmon fleet in California, which 30 years ago numbered 4,500 boats, has dwindled to fewer than 600.

"We're not making a living. There's a lot of guys dropping out," said Larry Collins, a salmon and crab fisher out of San Francisco who blames state water managers for his problems. "I'm struggling to make my payments."

Cause and effect

So far, most of the blame for the salmon's collapse has been placed on ocean conditions. Specifically, the Pacific Ocean in 2002 entered a warm phase that delays the onset of current "upwelling" off the West Coast and starves the marine ecosystem of nutrients and food.

Up and down the coast, salmon stocks were depressed with runs doing worse the farther south one looked, said Allen Grover, a biologist with the California Department of Fish and Game.

Since the Central Valley runs are the furthest south, it makes sense that they would appear the hardest hit, Grover said.

The Pacific Decadal Oscillation, which was discovered just 10 years ago, is a shifting ocean and atmospheric climate pattern that affects West Coast currents and salmon populations.

McIsaac and others say it is likely to be only part of the story for the Sacramento River fish, which took a sharper downturn than those in the Klamath River -- and last year's return on the Klamath was strong.

"It's not the same thing that happened on the Klamath River fish," McIsaac said.

Peter Moyle, a leading UC Davis expert on California's native fish, said a run of years with favorable ocean conditions might have masked problems upstream.

During good years in the ocean, baby salmon might have had a tough time as they swam downriver and through the Delta to rear and grow strong enough to survive in the ocean. But once they reached the open water, those survivors were able to thrive.

When ocean conditions soured, though, salmon were hit with a double whammy.

"It's quite likely that when ocean conditions got worse, suddenly you got this massive collapse," Moyle said. "That suggests the ocean conditions could no longer compensate for conditions upstream."

Although Moyle cautioned there are numerous possible explanations for the decline in salmon, "You can't dismiss the problems in the Delta and the problems with the diversion of water."

Uncertain future

The number of returning fall-run salmon in the Sacramento River last year -- fewer than 90,000 -- was the second-lowest ever. It represents a steep decline from recent years and wipes out gains made since the early 1990s, a span in which $1 billion was spent to improve conditions for Sacramento River salmon.

What's worse is the number of 2-year-old salmon that returned last year -- 2,000, or one-fourth of the 8,000 jacks that preceded the disastrous 2007 return.

There is some good news, however, in that the Pacific entered a cold phase last year, said Bill Peterson, an oceanographer at the National Oceanic and Atmospheric Administration.

Peterson is convinced that the ocean conditions and the poor upwelling in recent years is the most likely cause of the salmon's decline.

"The salmon guys, they look to the freshwater for all the answers," he said.

In 2005, for example, upwelling was badly disrupted and that resulted in widespread deaths of sea birds and other problems.

"At the time, we said there are going to be problems with salmon in two years, and here we are," he said.

Peterson added, though, that the Pacific Decadal Oscillation appears to be changing, possibly in response to a warming climate. The shifts have become more frequent and its effects on upwelling may be more severe.

"What we're wondering is whether last summer is the first of what we're going to see," he said. "We're getting really strong winds late in the upwelling season. If that's the case, that doesn't seem to be a good thing for salmon."

'Where the battle is'

At a meeting last week in Santa Rosa, a few hundred salmon fishers showed up to prepare for this week's meetings in Sacramento. Many expressed uncertainty about their future but no doubt about what is causing their problems -- water deliveries out of the Delta.

Several speakers urged the commercial fishers, recreational anglers, ocean fishers and river guides in the audience to stop battling over access to fish and instead unite against the water agencies they see as the bigger threat to the salmon because of the large amounts of water they pump out of the Delta.

"If we want to get our fisheries back, that's where the battle is," said Grader. "You can't continue taking 6 or 7 million acre-feet out of the estuary and expect it to survive."

Dave Sereni Sr., a recreational fisher from Santa Rosa, drew a comparison between the salmon collapses on the Sacramento and Klamath rivers by blaming both on upstream water users.

"The same exact thing that happened in the Klamath is happening in the Delta," said Sereni. "I'm not opposed to them closing, but if they're going to do that, they need to address the main problems."

Grader said the National Marine Fisheries Service, which regulates water diversions to protect salmon, has been too lax and urged members of the fishery management council, which sets fishing limits, to demand better protection for salmon.

"I'm asking this agency to become vertebrates. Grow a friggin' backbone," Grader said. "These years and years of silence are not enough. That's what we expect next week from you in Sacramento."

Mike Taugher covers natural resources. Reach him at 925-943-8257 or mtaugher@bayareanewsgroup.com.